(2.) Many (but certainly not all) expats do come here without relocation being covered, but everyone's circumstances are different.
I am in a technical role as well and my experience and anecdotal evidence that I have amassed over time suggests that technical folks are less inclined to ensure that they are being compensated properly than, say, more businessy types.
You used the word "haggle" in your OP and I won't read too much into it, but I hope that you actually view or can be persuaded to view the dance that you going through now with your prospective employer for what it is, a negotiation. Don't allow yourself to be made to feel as though you're haggling/quibbling over "minor" issues or to assert that you're making unreasonable demands (relocation to HK, and also from HK back to the UK, is not an unreasonable demand).
If I were you, I would (1.) buy a couple of highly-rated books on salary negotiation and skim through them, (2.) Google for relatively recent examples of other folks' expat packages, (3.) tally up the qualifications/qualities that make you uniquely suited for this role as well as the reasons that you're interested in taking the job, and (4.) get back in touch with the org making the offer with your counter offer. Be prepared to calmly and clearly explain why the benefits you're asking for are reasonable and be prepared to walk away.
Maybe they'll find a sucker who is willing to move to the opposite end of the world and back on his own dime and decline to negotiate further. In that case, you may be better off passing on the job anyway.